In mounting an electrical box for housing a switch, a receptacle, or a lighting fixture on a wall stud, a ceiling joist, or like structural member, it is important to have the rim of the box positioned at the right depth relative to the outer surface of the completed wall, whether that surface is formed by plaster, by plasterboard, by panelling, or by some other wall surfacing. It is usually desirable that the rim of the box be located so that it is recessed about 1/16 inch from the finished wall surface. The positioning of the electrical box is most critical for plasterboard and panelled walls, since these walls do not have the flexibility of thickness adjustment that is possible with a plastered wall. It is rather difficult and time-consuming for the electrician or other workman to mount the electrical box accurately on a wall stud or joist to achieve this end result.
In the past, there have been a variety of proposals for jig and gauge devices to determine the position of an electrical box for mounting on a wall stud. For the most part, these devices have been designed to determine both the height of the electrical box above the floor and the depth of the box rim relative to the outer face of a stud. The result has been apparatus that is too large, too complex, and too expensive for most electricians and other workmen. Devices of this kind are described in Phair U.S. Pat. No. 2,919,913, Briggs U.S. Pat. No. 2,956,798, Hodgson U.S. Pat. No. 2,962,281, Gianotta U.S. Pat. No. 2,990,172, Utley et al U.S. Pat. No. 3,436,070, Stickney U.S. Pat. No. 3,751,026, and Tarr U.S. Pat. No. 3,954,717. Copies of all of these patents accompany this application.
In most construction projects, the height of an electrical switch or receptacle above the floor is not critical; displacement of an inch or two above or below a desired height is of no consequence. Furthermore, height location is readily accomplished with an ordinary workman's measuring tape. Thus, the height gauge provisions of the more common prior art devices are really not necessary; they impose an economical burden on the workman or contractor and add unnecessarily to the bulk and weight of the tools that must be carried by the workman.
One prior art device evidences a more sensible approach, in that it omits any provision for determination of height of the electrical box above a floor and concentrates on the critical factor, the depth of box mounting. This device is described in Crawford U.S. Pat. No. 3,154,304. However, the Crawford device is still relatively complex and expensive, incorporating a plurality of grippers, mechanical adjustments, and other moving parts.
What is really needed is a simple hand tool or jig that can be carried conveniently by a workman and can be used, whenever required, for accurate positioning of an electrical box on a stud or joist so that precise alignment of the rim of the box with respect to the outer surface of the finished wall is assured. This hand tool should require no adjustments on the part of the electrician and should enable the workman to carry out the job using only the usual tools of the trade and the workman's own hands, with no adjustment necessary for the hand tool during use.